Elastic scattering angular distributions were measured for 46-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ over the ∼ 30°-110° range and for 41-MeV $\alpha$ particles over the ∼ 25°-150° range for the neighboring targets ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{28,29,30}{}_{}{}^{}\mathrm{Si}$. For $\alpha$ particles, $l=2\mathrm{}$ inelastic scattering data were also obtained at angles beyond ∼ 50°. For ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ the three Si targets yield similar angular distributions that are different from that of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ at angles larger than ∼ 55°. The elastic $\alpha$-particle data supplement earlier back angle data to yield almost complete angular distributions. The ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ $\alpha$-particle elastic angular distribution exhibits an anamoly in the 80°-150° region. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ data were fitted by optical model potentials with either volume or surface absorption. To fit all of the $\alpha$-particle elastic scattering data, potentials with both volume and surface absorption, with separate geometry parameters, were needed. Distorted-wave Born-approximation analyses of the $\alpha$-particle inelastic scattering data yield values of ${\beta }_2$ that are in reasonable agreement with values obtained from analyses of scattering at other energies and incident particles.

NUCLEAR REACTIONS (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$) at MeV and ($\alpha , {\alpha }^{\prime }$) at 41 MeV from, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{28,29,30,}{}_{}{}^{}\mathrm{Si}$; enriched targets. Measured $\sigma \left(\theta \right)$; performed optical model and DWBA analyses; deduced scattering potentials and ${\beta }_2$ values.

• Received 15 November 1977

DOI:https://doi.org/10.1103/PhysRevC.18.621